Well, depending on what you're doing, AE sometimes has to use a lot of RAM, but sometimes it just has to sit, think & calculate.
If you're convinced AE is just plain acting weird, here are common things that alleviate a lot of weirdness:
Dave's Stock Answer #1:
If the footage you imported into AE is
any kind of the following -- footage in an HDV acquisition codec, MPEG1, MPEG2, AVCHD, mp4, mts, m2t, H.261 or H.264 -- you need to convert it to a different codec.
These kinds of footage use temporal, or interframe compression. They have keyframes at regular intervals, containing complete frame information. However, the frames in between do NOT have complete information. Interframe codecs toss out duplicated information.
In order to maintain peak rendering efficiency, AE needs complete information for each and every frame. But because these kinds of footage contain only partial information, AE freaks out, resulting in a wide variety of problems.
Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA